1. Field of the Invention
The present invention relates to a pod used to store and carry substrates or wafers, and particularly, to the structure of a pod that is easy to clean, a method of cleaning a pod, an apparatus for cleaning a pod, and an apparatus for processing substrates.
2. Description of the Related Art
Generally, substrates or wafers made of, for example, silicon (Si) are stored and carried in wafer cassettes during manufacturing. Each wafer cassette carries 13 or 25 wafers. The wafer cassettes with wafers are transferred between processing apparatuses such as film forming and etching apparatuses during manufacturing. A wafer/substrate transferring system that employs the wafer cassettes is called a cassette-to-cassette system.
FIG. 25A shows a conventional open-type wafer cassette 800. The cassette 800 consists of a top plate 820, a bottom plate 810, and three posts that support the top and bottom plates 820 and 810. The posts 830 have grooves for supporting wafers, and the post 840 serves as a stopper for preventing the wafers from dropping.
In place of such wafer cassettes, pods have been studied to store and carry substrates or wafers, to meet needs for highly integrated fine devices to be produced from the substrates or wafers.
FIGS. 25B, 25C, and 25D show pods presently studied. Each pod consists of a pod body and a cover. The pod body is a box having an opening for taking in and out wafers, and the cover closes the opening of the pod body. The pod of FIG. 25B has a bottom opening that is closed by a cover 920. The pods of FIGS. 25C and 25D have side openings that are closed by covers 921 and 922, respectively. The pods of FIGS. 25B and 25D store the conventional open-type wafer cassettes with wafers. The pod of FIG. 25C has grooves on the inner wall thereof, to directly hold wafers without a wafer cassette.
The pods are capable of storing and carrying wafers in a closed dust-free space, thereby improving the yield of semiconductor products to be produced from the wafers.
Recent wafers are large in diameter, size, and weight to improve productivity. For these large wafers, the conventional wafer cassettes involve a risk of dropping the wafers during carriage, and therefore, the pods are preferable for such large wafers.
The pods are advantageous in keeping dust-free environment for wafers and securing safe carriage. The pods, however, have some problems. This will be explained.
The open wafer cassettes can be washed while holding wafers. On the other hand, wafers stored in closed pods are unable to wash. To wash them, they must be taken out of the pods. This means that the pods themselves are rarely washed during wafer processing.
As a result, the insides of the pods are gradually contaminated. This deteriorates the cleanliness of wafers stored therein, thereby lowering the yield of semiconductor products to be produced from the wafers.
The pods may be washed separately from the wafers during wafer processing. To wash large pods that store 200-mm to 300-mm diameter wafers, a large washing tank is needed. FIG. 26A shows a washing tank 950 for washing a pod 911. The tank 950 must be larger than the pod 911, and if the pod 911 is large, the tank 950 must be very large. FIG. 26B shows a pod washing apparatus having a washing tank 960 and a dryer chamber 980. This apparatus is very large. In a limited space in a clean room, such a large apparatus is hardly acceptable.